The sense of taste is intimately involved in food selection, identification, digestion and metabolism. Loss or alteration of this chemo-sense can lead to nutritional and metabolic compromises and to a decrease in the quality of life. The overall goals of our work seek an understanding of the molecular-biochemical events at the taste receptor cell level so that therapies for deficiencies in the sense of taste can be approached from knowledgeable and rational basis. The current proposal emphasizes a research approach to allow characterization of the receptors, evaluation of the transduction sequences in taste and purification of taste receptors. The experimental model, I. punctatus, possesses unique, highly sensitive and identifiable receptors for various chemostimulatory amino acids. This model has proved very valuable in understanding the fundamental mechanisms of taste and olfaction. The specific aims of this proposal seek to 1) describe the pharmacology of taste receptor sites through receptor binding techniques using newly available agonists/antagonists to these receptors; 2) investigate the transduction sequences by characterizing second messenger-forming enzyme systems (including adenylate and guanylate cyclase, phospholipase C and phospholipase A2) and by studying the reconstituted taste stimulus- activated (ligand-gated) cation channels from taste cells; 3) characterize the receptor link to second messenger formation via GTP- binding regulatory proteins; and 4) purify and characterize these taste receptors. These aims will be accomplished using both biochemical and neurophysiological approaches. Knowledge of receptor macromolecules. Of particular interest are recent observations indicating that, of the two main taste receptor pathways i this animal, one apparently operates via production of second messengers, the other via a ligand-gated cation receptor. The proposed studies will allow a detailed examination of these two mechanisms, ones which we hypothesize are also active in mammalian receptor systems. Upon completion of these studies, we will have evaluated receptor pharmacology, determined the relative importance to taste of several second messenger and transduction systems and purified taste receptor proteins for study in the reconstituted state.